Electric air heater



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Nov. 25, 1952 Flled May 4 1950 N0V 25, 1952 J. w. cARTlNHoUR ELECTRICAIR HEATER 2 SHEETS--SHEET 2 Filed May 4, 1950 Gttorneg Snventor @@QMWPatented Nov. 25, i 1952 ELECTRIC AIR HEATER John W. Cartinhour,Baldwin, N. Y., assignor to Foster Wheeler Corporation, New York, N. Y.,a corporation of New York Application May 4, 1950, Serial No. 159,937

Claims.

This invention relates to a heat exchanger for air or other uids andmore particularly to an electric air heater.

In certain high pressure, high temperature service, utilizing largequantities of air for relatively short periods of time, for exampleonly, the supply of air at approximately 104:0o F. and 3000 p. s. i. g.with entering -conditions at 650 F. and 3030 p. s. i. g., the heatermust be capable of being placed in service at its full capacity in amatter of a few seconds and must maintain steady conditions thereafter.

This requires a heater having unique features which are objects of thisinvention and which may be grouped as follows.

`(1) Features enabling the exchanger to perform according torequirements;

(2) Features providing for safe operation; and

(3) Features contributing to an economic solution of the problem.

Single features do not necessarily contribute to only one of the groupsand in several cases a feature contributes to all three.

The necessity for rapid starting combined with steady operatingconditions is met in this invention by utilizing electric power as asource of heat. It can be made available with extreme rapidity and itsrate of input can be controlled with a high degree of accuracy. Further,in order to reduce the time required to make heat available to aminimum, the heat storage capacity of the heating elements must berelatively small. This condition is satisfied by the use of highvoltages and light resistive conductors. Moreover the relatively smallmass of these resistive conductors alone contributes to the -economy ofthe structural design.

Although the primary purpose of the heating elements is to heat the airor other uid to the desired temperatures, it is important that theyaccomplish their function safety. Therefore, these elements must bearranged so that the danger of overheating is minimized. For this reasonthe heating elements utilized herein are tubular in form and arranged sothat the air or other fluid to be heated iiows through them. Thepressure drop through the tubular elements is sufficient to assure evendistribution of flow through the various tubes, and the lcw rate pertube is high enough to provide relatively high heat transfercoeiiicients. Thus the use of small, light heating elements contributesto all three of the desirable unique features grouped hereinabove.

The tubular heating elements are enclosed in a (Cl. 21S-39) 2 A metallicshell, in a manner to be described, to provide appropriate distributionand flow of air through the elements. Since all metals lose strength atelevated temperatures, it is desirable to keep the shell temperatures aslow as possible. For this reason the cool air of fluid to be heated isdirected in such a way inside of the shell, by arrangements to bedescribed, as to keep the shell at a uniformly low temperature. Thisreduces the cost of the shell by reducing its required thickness and,also, by eliminating the necessity for use of high-alloy materials forthe shell. It also contributes to the safety of the shell or vessel byreducing thermal stresses which under the rapid starting conditionsmentioned herein might eventually cause cracking of the shell and aserious operating failure. In addition, the maintenance of uniform shelltemperature at gasket joints in the shell reduces the possibility of airor fluid leakage through them.

Other objects and novel features of the invention include the provisionof structure adaptable for providing heat exchange between differentiiuids at diiferent temperatures and also of structure adaptable forelectrical heating of iiuids other than air having proper dielectricproper-' Fig. 4 is a fragmentary longitudinal section on` an enlargedscale taken along line 4-4 of Fig. 2

illustrating details of construction, and, also, Viewed in the directionof the arrows;

Fig. 5 is a fragmentary transverse section taken along line 5-5 of Fig.4 also viewed in the direction of the arrows; and

Fig. 6 is an isometric view in diagrammatic form of the heating tubearrangement and electrical circuit involved.

Referring to the drawings, i0 denotes a hollow shell of metal or otherdeisrable material which is provided at its opposite ends with tubularend members i l and I2 of larger overall cross sectional dimensions thanthat of shell IIJ and each having two differently dimensioned internalportions lla, Hb and |2a, lZb respectively each:

diierent from that of the internal dimensions of shell in to define therespective shoulders IIc, IId and I2C, I2d. The end members II and I2are secured respectively to the opposite ends of shell IB as by weldingor the like at I3 and I4.

The inner wall of shell ID is provided with a snugly tting tubular liner|5 preferably of sheet metal. ThisV liner I5 isv optional it shell I3 isitself of metal suitable for the intended purposes. Metal closuremembers I6, 16a tting within the recesses IIa and |2a with sealinggaskets G abut the respective shoulders I|c and I2Cv and areY tightenedagainst the gaskets G and secured in place as by bolts and nuts I1, I'8.External re inforcements 20, 2| are provided for the respective closuremembers I6, |611. and these are held securely against the latter bysegmental locking rings 22, 23 tting edgewise respectively" in theannular grooves 24, 25 in portions IIa and |2a of members and I2 andbolted tothe respective reinforcementsrz, 2| by bolts-25.

A- tubular shell 28 of sheetmetalor the like having smaller crosssectionalA external dimensionsthan the inner cross sectional dimensionsof'A liner l5 or inner dimension of shellV Ill is loY catedV in acentralized position Within shellV Il),Y one-endY projecting into theportion 12b ofend member I2. The shell 23- is provided atvarious`external-points withV spacing fins or lugs 29 which centralize itrelativerto liner I5 and shell I0- throughout its lengthr so that shell28 and lining l5 define an` annular space Sextending fromthe shoulderIZ-d-to the far end of shell28. where the space Sv communicates with achamber portion C of shell I 0.

.A- transversely extending partition 30 divides the inner shell int= atube bearing compartment D toone side ofy the. partitionl 30 anda coldair space E at its opposite side. Openings 3| in. the wallof shell 28Aprovide communication between spaces. S and E for purposes presently tobe described.

Aninlet nozzle- 33, preferably having a lining 34;, is secu-red asbywelding or the like at 35 about an opening 36 provided in shell I0 andits lining I and communicates with the annular space S. y An outletnozzle 31 preferably having a lining- 3&is1secured as bywelding or thelike at 39 about an opening 40 communicating with space S. An innershell or tube 4I of smaller diameter than lining 3i!Y and ldefining withit an annular space passageway H- extends from the outer end. of nozzle3`| inwardly and is secured as by welding or the like at 42 about anopening l43l in shell 2,8 which communicates with space D 'ofA thelatter. Thus all internal surfaces of the shell Ill and its ends are insurface contact withairv or uid at itsv cool enteringtemperature and theshell. I0 remains substantially atv this temperature, during use;

Transversely extending metallic tube supports 45each fitting within anannular recess of aperipheral supportingY ring 55 are positioned atspaced apart points within the shell 28, the rings 45 fitting snugly butmovably the internal diameter of shell 28. The particular ring @E of thetube support 45 in closest proximity to partitionV 35 abuts an annularsegmental ring ll'll secured as by lugs' il or the like to the innerlsurface of shell 28. This ring 4l serves as a limit stop. The outermostsupporting ring t5 adjacent the opposite end of shell 28 is providedwith longitudinally extending expansion rods 48 which fit slidably vinopenings provided in guide flanges @soldered or the like to the shell28.

Each tube support 45 has a like number of identically arranged openings50 (Fig. 4) in each of which a tubular bushing 5| of electric insulatingmaterial is mounted. Tubes 52 of electrical resistor material, forexample, nickelchromium alloy, or other equivalent electric resistormaterial are threaded longitudinally through axially aligned bushings 5|in the respective tube supports 45, one end of each tube 52communicating with chamber C, and the opposite end of each tube 52communicating with chamber D. The tube support plates 45 t rings46,*.andthelatter it the inner surface of shell 28` and, similarly,Abushings 5I t openings 50 and tubes 52: fity bushings 5I suicientlyclosely to limit leakage of air from space C to space D through'spaceFt'o a very small quantity, but the nts are' not close enough toprevent relative expansion or contraction of parts.

Theends of. all resistor tubes 52 projecting into chamber C in' eachhorizontal row of. tubes. (Fig. 6) are electrically interconnectedY bydistribu-l tors` 53- and all theA latter are electrically connectedto abustiY which in turn is connectedby a metalconductor` 55to af terminal56 carriedby an insulator 51 that in turn extends outwardly of theAlining I5 and shell I0 through an opening that isV sealed appropriatelyaround its edges at 5.3. The' other ends of allr tubes 52 projectinginto.- chamber Dl ineach horizontal row are electrically interconnectedYby` distributors. 59'., and the latter are electrically connected to abus 6D Whichis, for example, grounded by connection at 6I with the shell28v which latter is connected electrically by the weldatAZ to theshell-Mwhich is in contact with. the grounded outlet nozzle. 3l.Y

Allthe tubes 52` are thus` connected in electrical parallel andmay besuppliedfrom .a common power source P connected toV the terminal 55andto ground. Appropriate Voltage andcurrentv controls. (not shown)r areconnected in the power circuit in the usual manner. While electricalparallel connection for tubes 52 is shown, it is to be understood thatthe. electricaly connection of the tubes 52, also, maybe either seriesor series-parallel depending uponthe type of electric power available atthe place of use; the requirement' being that electric currentv flow invtheA tubes will be sufficient to heat them to necessary temperatures'toproduce desired heatingv of the air or other fluidi flowing through there-f sistor' tubes 52.

Operation Electrical. power' l? is connected to the tubesy 52 asdescribed. Air is introduced through noz.-Y zle. 33 andis rst directedtoflow in space S between lining l5 and shell 28 as an. envelope of air tomaintain substantially uniform temperature of` the outer shell il andits lining |5- to space'or chamber C whence it flows through each of theelectrically heated tubes '52 to space or chamber D being heated in itspassage through the tubes; From chamber D the heated air flows outwardlythrough tube I in nozzle 3?. A small portion of the cold air enteringnozzle 3'3 also flows from passage S through some of the openings 3I'into space or chamber E and from the latter outwardly through others ofthe openings 3| and through the annular space H and rejoins the heatedair owing in tube 4I through openings 'lb in the wall of the latter. Thecool air in chamber E and in space I-I acts to keep the hot end of shellI0 andv outlet nozzle 3l at substantlally the same uniform temperatureas shell I0.

Although the invention has been described as an air heater, it is notlimited in its application to air. Any fluid having proper dielectricproperties can be heated in the exchanger described. The heaterconstructed and operated as described embodies all features outlined atthe outset of this specification. The shell 28, members 45 and partition30 act as bailies to direct the air or iluid in proper direction asdescribed.

Modification With slight modification, and without the use of electricheating, the device can be utilized to provide heat exchange between anycold and any hot fluid. In such case, the material of tubes 52 need notbe of electric resistor material, but may be of any other metal.Electric connections to the tubes can be eliminated and the end tubesupports 45 and their rings 45 provide leak proof seals at opposite endsof tubes 52 and shell 23 so that compartment or chamber F is sealed 01Tfrom chambers C and D. An inlet nozzle and an outlet nozzle eachcommunicating with chamber F are provided. One of the two iluids iscirculated via nozzle 33 through space S, chamber C, tubes 52, chamber Dand outlet nozzle 3'! as previously7 described. The other of the twouids is fed into chamber F around the external surfaces of tubes 52 inheat exchange relationship with the fluid flowing through the lattertubes and finally out through the second outlet nozzle. Relative flow ofthe two fluids may be in counter current direction or the same directionas desired.

While specific embodiments of the invention have been disclosed,variations in structural detail within the scope of the claims arepossible and are contemplated. There is no intention therefore oflimitation to the exact details shown and described.

What is claimed is:

l. Apparatus for heating air or other fluids comprising an outerelongated shell, removable cover members at opposite ends of said shell,means for securing said cover members in fluidtight relationship withthe outer shell, an inner shell supported within and extendinglongitudinally of the outer shell, the inner shell being so dimensionedand positioned within the outer shell as to denne a iiuid flowpassageway around the inner shell between the inner surface of the outershell and the cuter surface of the inner shell, tube supports spacedfrom one another and spanning in a duid-tight manner the crosssectionalarea of the inner shell and in spaced relationship with the oppositeends of the outer shell, one of the tube supports dening one side of afluid inlet chamber within the outer shell between one end of said outershell and said one support, the inlet chamber being in communica-- tionwith the lluid passageway, a partition spanning the cross-sectional areaof the inner shell intermediate the opposite end oi the outer shell andthe other tube support, thereby deiining one end of a heated uid outletcompartment between said other tube support and the partition and a coolfluid space between said opposite end of the outer shell and saidpartition, the cool iluid space being in communication with said fluidnow passageway to receive fluid therefrom, a fluid inlet nozzle incommunication with the uid flow passageway adjacent said opposite end, afluid outlet nozzle in communication withv the outlet compartment atsaid opposite end, tubes carried by said supports and extending inspaced relationship with one another longitudinally through the innershell with their opposite ends extending into the respective inlet andoutlet chambers, electrical connections interconnecting all the tubes atone end to a common conductor, electrical connections interconnectingall the tubes at the other end to a second common conductor, and meansfor connecting the said common conductors to a source of electric powerwhereby said tubes may be heated electrically and whereby the fluid tobe heated will be directed from the inlet nozzle through the iiuidpassageway in surface contact with the inner and outer shells and intosaid inlet chamber, then through the tubes being heated in iiowtherethrough, and into said heated fluid outlet compartment chamber andthereafter through the outlet nozzle.

2. Apparatus for heating air or other fluids comprising a cylindricallyshaped outer shell, removable cover members at opposite ends of saidshell, means for securing said cover members in fluid-tight relationshipwith the outer shell, a cylindrically shaped inner shell supportedwithin and extending axially of the outer shell, the inner shell beingof a lesser diameter than and so positioned within the outer shell as todefine a fluid ilow passageway around the inner shell between the innersurface of the outer shell and the outer surface of the inner shell,tube supports spaced from one another and spanning in a huid-tightmanner the cross-sectional area of the inner shell and in spacedrelationship with the opposite ends of the outer shell, one of the tubesupports deiining one side of a fluid inlet chamber within the outershell between one end of said outer shell and said one support, theinlet chamber being in communication with the fluid passageway, apartition spanning the cross-sectional area of the inner shellintermediate the opposite end of the outer shell and the other tubesupport, thereby deiining one end of a heated iluid outlet compartmentbetween said other tube support and the partition and a cool fluid spacebetween said opposite end of the outer shell and said partition, thecool iluid space being in communication with said fluid now passagewayto receive fluid therefrom, a fluid inlet nozzle in communication withthe fluid flow passageway adjacent said opposite end, a fluid outletnozzle in communication with the outlet compartment at said oppositeend, tubes carried by said supports and extending in spaced relationshipwith one another longitudinally through the inner shell with theiropposite ends extending into the respective inlet and outlet chambers,electrical connections interconnecting all the tubes at one end to acommon conductor, electrical connections interconnecting all the tubesat the other end to a second common conductor, and means for connectingthe said common conductors to a source of electric power whereby saidtubes may be heated electrically and whereby the uid to be heated willbe directed from the inlet nozzle through the fluid passageway insurface contact with the inner and outer shells and into said inletchamber, then through the tubes being heated in flow therethrough, andinto said heated fluid outlet compartment chamber and thereafter throughthe outlet nozzle.

3. Apparatus for heating air or other fluids comprising an outerelongated shell, removable cover members at opposite ends of said shell;

means for' securing saldi cover members influidtight relationship withthe outer shell,v an inner shell supported within and extending'longitudinally of the outer shell, the innerl shell being so dimensionedand positioned within the outer shell as to define a iiuid flowpassageway around the inner shell between the innerv surface of theouter shell and the outer surface of the inner shell, tube supportsspaced from one anotherA and spanning'in a huid-tight manner thecross-sectional area of the innery shell andy in spaced relationshipwith'the opposite ends of the outer shell, one of the tube supportsdefining one side of a iluid inletvchamber within the outer shellbetween one end ofv said outer shell and said one support, the

inlet chamber' being in communication with the il'uld passageway, apartition spanning the crosssectional areaof the inner shellintermediate the opposite end of the outer shellV and the other tubesupport, thereby denning one end of a heated fluid outlet compartmentbetween said other tube support and the partition andl a cool fluidspace between said opposite end of the outer shell and said partition,the coolud space being in communication with said fluid iiow passagewayto receive fluid therefrom, a. uid inlet nozzle in communication withthe fluid flow passageway adjacent said opposite end, a iiuid outletnozzle in communication with the outlet compartment at said oppositeend,v said outlet nozzle oomprising an inner sleeve so dimensioned andpositioned within the nozzle as to define a flow path around said sleevebetween the outer periphery thereof and the nozzle, said sleeve being incommunication at the inlet end thereof with the heated fluid compartmentand at the outlet end withr the nozzle outlet, the flow path beingl incommunication at one end thereof with said fluid passageway to receivefluid therefrom and at the opposite end with said nozzle outlet, tubescarried by said supports and extending in spaced relationship with oneanother longitudinally through the inner shell with their opposite endsextending into the respective inlet and outlet chambers, electricalvconnections interconnecting all the tubes at one end to a commonconductor, electrical connections interconnecting all the tubes at theother end to a second common conductor, and means for connecting thesaid common conductors to a source of electric power whereby said tubesmay be heated electrically and whereby the fluid to be heated will bedirected from the inlet nozzle through the fluid passageway in surfacecontact with the inner and outer shells and into said inlet chamber,then through the tubes being heated in flow therethrough, and into saidheated fluid outlet compartment chamber and thereafter through the innersleeve of the outlet nozzle.

4. Apparatus for heating air or other fluids comprising an outerelongated shell, removable cover members at opposite ends of said shell,means for securing said cover members in fluidtight relationship withthe outer shell, an inner shell supported within and extendinglongitudinally of the outer shell, the inner shell being so dimensionedand positioned within the outer shell as to denne a fluid flowpassageway around the inner shell between the inner surface of the outershell and the outer surface of the inner shell, tube supports spacedfrom one another and spanning in a fluid-tight manner thecross-sectional area of the inner shell and in spaced relationship withthe opposite ends of the outer shell, one of the. tube supports definingone side of a uid inlet chamber within the outer shell betweenV oneVend, of said outer shell and said one support, the inlet'. chamberbeingl in communication with the fluid passageway, a partition spanningthe crosssectional area of the inner shell intermediate the opposite endof the outer shell and the other tube support, thereby defining one endof a` heated fluid outlet compartment between said other tube supportand the partition and a cool fluid space between said opposite end ofthe outer shell and` said partition, the cool iiuid space being inrcommunication with said uid flow passageway to receive iluid therefrom,a fluid inlet nozzle in communication with the iiuid flow passagewayadjacent said opposite-end, a iiuid outlet nozzle in communication withthe outlet compartment at` said opposite end, tubes carried' by saidsupportsand extending in spaced relationship with oneanotherlongitudinally through the inner shell with their opposite endsextending into the respective inlet and outlet chambers, electricalconnections interconnecting all the tubes adjacent one end of the outershell to a common conductor, electrical connections interconnecting allthe tubes adjacent the other end of said shell to a second commonconductor, means at said oneend of the outer shell and extending intosaid inlet chamber for connecting the common conductor at said one endto a source of electric power, and means for connecting the commonconductor at said other end to the source, whereby said tubes may beheated electrically and whereby the fluid to be heated will be directedfrom the inlet nozzle through the fluid passageway in surface Contactwith the inner and outer shells and into said inlet chamber, thenthrough the tubes being heated in flow therethrough, and into saidheated fluid outlet compartment chamber and thereafter through theoutlet nozzle.

5. Apparatus for heating air or other iluids comprising a cylindricallyshaped outer shell, removable cover members at opposite ends of saidshell, means for securing said cover members in fluid-tight relationshipwith the outer shell, a cylindrically shaped inner shell supportedwithin and extending axially of the outer shell, the inner shell beingof a lesser diameter than and so positioned within the outer shell as todefine a fluid flow passageway around the inner shell between the innersurface of the outer shell and the outer surface of the inner shell,tube supports spaced from one another and spanning in a fluid-tightmanner the cross-sectional area of the inner shell and in spacedrelationship with the opposite ends of the outer shell, one of the tubesupports defining one side of a fluid inlet chamber within the outershell between one end of said outer shell and said one support, theinlet chamber being in commiu'n'cation with the fluid passageway, apartition spanning the cross-sectional area of the inner shellintermediate the opposite end of the outer shell and the other tubesupport, thereby defining one end of a heated fluid outlet compartmentbetween said other tube support and the partition and a cool fluid spacebetween said opposite end of the outer shell and said partition, thecool iluid space being in communication with said iluid flow passagewayto receive fluid therefrom, a fluid inlet nozzle in communication withthe fluid now passageway adjacent said opposite end, a fluid outletnozzle in communication with the outlet compartment: at said oppositeend, said outlet nozzle comprising an inner'sleeve so dimensioned andvpositioned within the 'nozzles as to define a now path around saidsleeve between the outer periphery thereof and the nozzle, said sleevebeing in communication at the inlet end thereof with the heated fluidcompartment and at the outlet end with the nozzle outlet, the low pathbeing in communication at one end thereof with said fluid passageway toreceive fluid therefrom and at the opposite end with said nozzle outlet,tubes carried by said supports and extending in spaced relationship withone another longitudinally through the inner shell with their oppositeends extending into the respective inlet and outlet chambers, electricalconnections interconnecting all the tubes adjacent one end of the outershell to a common conductor, electrical connections interconnecting allthe tubes adjacent the other end of said shell to a second commonconductor, means at said one end of the outer shell and extending intosaid inlet chamber for connecting the common conductor at said one endto a source of electric power, and means for connecting the commonconductor at said other end to the source, whereby said tubes 10 may beheated electrically and whereby the fluid to be heated will be directedfrom the inlet nozzle through the fluid passageway in surface contactwith the inner and outer shells and into said inlet chamber, thenthrough the tubes being heated in flow therethrough, and into saidheated fluid outlet compartment chamber and thereafter through the innersleeve of the outlet nozzle.

JOHN W. CARTINEIOUR.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,356,818 Hadaway Oct. 25, 19201,615,166 Cowles Jan. 18, 1927 1,727,584 Carleton Sept. 19, 19291,787,801 Swoboda et al Jan. 6, 1931 1,926,958 Peterson Sept. 12, 19331,985,280 Carleton Dec. 25, 1934

